Dispensers for delivering a predefined volume of beverage are well known. A common example is an “Optic” (registered trade mark of Gaskell and Chambers Limited) device fitted to an inverted spirit bottle (e.g. gin, whiskey, etc). Such a device includes a small chamber of measured volume with a spring-loaded mechanism that closes communication between the chamber and bottle as the chamber is opened to release its measured volume under gravity into a glass. As the chamber closes to the outside environment communication with the bottle is again opened, filling the volume ready for its next use.
A conventional Optic is not suited for use with carbonated beverages because the empty chamber is effectively at atmospheric pressure when it is opened to communication with the bottle. The pressure drop on the beverage as it flows to the chamber causes the gas to bubble out of solution and subsequently lose carbonation and perceived loss in product quality over time. Furthermore, the pressurised liquid in the chamber is prone to squirting when being dispensed rather than pouring smoothly.